The present invention generally relates to a transmission power control method and apparatus for mobile communication system which controls the transmission power between the base station and mobile terminal of a mobile communication system, and particularly to the effective technology suitable for use in the transmission power control method and apparatus for mobile communication system which controls the transmission power in accordance with the change of signals received between the base station and mobile terminal of the mobile communication systems such as TDD-SS (Time Division Duplex-Spread Spectrum) and FDD (Frequency Division Duplex) systems.
There is a conventional mobile communication system for transmitting and receiving data by radio between base stations and mobile terminals. This mobile communication system employs different carrier frequencies for the up link on which signals are transmitted from a mobile terminal to the base station and for the down link on which signals are transmitted from the base station to the mobile terminal by the for example
The signal transmitted and received between the base station and mobile terminal of this mobile communication system is attenuated along the distance between the base station and mobile terminal, and by obstacles present therebetween, and fluctuated by the fading due to the interference between the direct wave and the reflected wave, or the like.
In order to compensate the fluctuation due to the fading in the signal transmitted and received between the base station and the mobile terminal which is dependent upon the carrier frequency, the transmission power in the FDD mobile communication system is controlled by closed-loop control. For example, the IS-95 specifications apply up link transmission power control of the FDD system which controls the transmission power of the terminal. The technique on the scheme of the FDD down link power control is proposed in U.S. Pat. 5,559,790 entitled xe2x80x9cSpread Spectrum Communication System and Transmission Power Control Method Thereforxe2x80x9d invented by Yano, et al., assigned to the present assignee and issued Sep. 24, 1996. In addition, another technique on the information of the up link power control is proposed in a copending U.S. patent application Ser. No. 08/690,819 entitled xe2x80x9cCDMA Mobile Communication System and Communication Methodxe2x80x9d by those inventors, assigned to the present assignee and filed on Aug. 1, 1996. The disclosure of the above U.S. application, and the continuation application, Ser. No. 08/678,656 of the above U.S. patent, filed on Jul. 11, 1996, are incorporated in the disclosure of this application by reference.
Whether the mobile communication system is of CDMA-FDD or CDMA-TDD, the following problem is caused when transmission power control is performed through the transmission path between the mobile terminal and the base station. In other words, when the attenuation of data in the transmission path between the base station and a particular mobile terminal is temporarily increased, the base station transmits signals with an extremely higher power in accordance with the transmission power control, and thus interferes with other mobile terminals. In addition, when the transmission power from a mobile terminal, on the contrary, is excessively risen, it also obstructs or interferes with other base stations.
Moreover, in the FDD mobile communication system, since the closed loop control is still performed in which the transmission power on the up link is controlled by the mobile terminal in accordance with the up link power control information obtained at the base station, while that on the down link is controlled by the base station in accordance with the down link power control information attained at the mobile terminal, there is the problem that it takes a long time to control the transmission power.
Accordingly, it is an object of the invention to provide a transmission power control method and apparatus for the mobile communication system, by which the transmission power can be prevented from being wasted and from obstructing other stations.
It is another object of the invention to provide a transmission power control method and apparatus for the mobile communication system, which can quickly compensate for the signal fluctuation occurring on the up link that is provided from the mobile terminal to the base station.
It is still another object of the invention to provide a transmission power control method and apparatus for the mobile communication system, which can quickly compensate for the signal fluctuation caused on the down link that is provided from the base station to the mobile terminal.
According to the concept of the present invention, there is provided a transmission power control method and apparatus for controlling the power of a signal transmitted between a base station and a mobile terminal, which includes: means for detecting a signal fluctuation occurring on a down link or up link; means for generating power control information in order to compensate for the signal fluctuation occurring on the up link or down link on the basis of the detected signal fluctuation; means for compensating for the power of the signal transmitted on the up link or down link on the basis of the information; and means for comparing the generated power control information and a predetermined permissible compensated value, temporarily stopping the transmission if the power control information is larger than a predetermined permissible compensation value as a result of the comparison, and compensating for the transmission power if the power control information is equal to or smaller than the predetermined permissible compensation value, all the above means being provided in the base station or mobile terminal. The above idea is useful particularly when a signal of data packets is transmitted between the base station and the mobile terminal. In this idea, unlike speech service, when the transmission power of the packet is requested to be more than a predetermined value, and when it will be too intense to interfere with other base stations or mobile terminals in a mobile communication system, the transmission is temporarily stopped, and a certain time later it resumes, in which case it has been confirmed by the inventors that the communications are not disturbed at all.
In order to achieve the above objects, the present invention proposes the following typical aspects.
(1) A transmission power control method for controlling the power of a signal transmitted between the base station and the mobile terminal which constitute a mobile communication system, comprises the steps of detecting a signal fluctuation occurring on a down link that is provided to transmit a signal from the base station to the mobile terminal, generating power control information for compensating for a signal fluctuation on an up link on the basis of the detected signal fluctuation, compensating for the transmission power of the signal transmitted on the up link from the mobile terminal to the base station on the basis of the generated power control information, and transmitting the power control information used for compensating for the transmission power, and transmitting the signal of which the power has been compensated, from the mobile terminal to the base station.
In the transmission power control method for the mobile communication system, the mobile terminal that communicates with the base station receives a signal transmitted on a down link from the base station to the mobile terminal, for example, a pilot signal transmitted on a pilot channel.
Then, the mobile terminal detects a signal fluctuation, such as the attenuation, occurring on the down link due to the fading and distance or an obstacle along the channel.
The mobile terminal assumes that the detected signal fluctuation in the down link similarly occurs in the up link on which a signal is transmitted from the mobile terminal to the base station, and generates power control information to compensate for the signal fluctuation occurring on the up link.
Then, the mobile terminal modifies the transmission power of the signal to be transmitted on the up link from the mobile terminal to the base station on the basis of the generated power control information.
In addition, the mobile terminal also transmits he power control information used for compensating for he transmission power from the mobile terminal to the base station.
Thus, according to the transmission power control method for the mobile communication system, since the mobile terminal compensates for the signal fluctuation occurring on the up link for the transmission from the mobile terminal to the base station by detecting the signal fluctuation occurring on the down link for the transmission from the base station to the mobile terminal, it is possible to quickly compensate for the signal fluctuation occurring on the up link for the transmission from the mobile terminal to the base station.
(2) A transmission power control method for the mobile communication system, according to the aspect (1), wherein the base terminal that communicates with the mobile terminal has functions to receive the power control information transmitted from the mobile terminal to the base station, detect a signal fluctuation occurring on the up link for the transmission from the mobile terminal to the base station, generate power control information to compensate for the signal fluctuation occurring on the down link on the basis of the detected signal fluctuation and the power control information sent from the mobile terminal, and compensate for the transmission power of the signal to be transmitted on the down link from the base station to the mobile terminal on the basis of the generated power control information.
The base station receives a signal sent on the up link from the mobile terminal to the base station, for example, a signal of reservation packets and data packets transmitted on a reservation channel and transmission channel.
The base station detects the signal fluctuation occurring on the up link for the transmission from the mobile terminal to the base station, and generate power control information to compensate for the signal fluctuation occurring on the down link on the basis of the detected signal fluctuation and the power control information sent from the mobile terminal.
Then, the base station modifies the transmission power of the signal transmitted on the down link from the base station to the mobile terminal on the basis of the generated power control information.
Thus, according to the transmission power control method for the mobile communication system, since the base station detects the signal fluctuation occurring on the up link for the transmission from the mobile terminal to the base station, and compensates for the signal fluctuation occurring on the down link for the transmission from the base station,to the mobile terminal, it is possible to quickly compensate for the signal fluctuation occurring on the down link for the transmission from the base station to the mobile terminal.
(3) A transmission power control method for the mobile communication system, according to the aspect (1) or (2), further comprising the steps of comparing the generated power control information and a maximum permissible modification or compensation value, temporarily stopping the transmission if the generated power control information is larger than the maximum permissible compensation value, and compensating for the transmission power if the generated power control information is equal to or smaller than the maximum permissible compensation value.
More specifically, the base station or the mobile terminal compares the generated associated power control information and the maximum permissible compensation value of the base station or the mobile terminal, temporarily stopping the transmission if the generated power control information is larger than the maximum permissible compensation value until the next time slot comes.
If the generated power control information is equal to or smaller than the maximum permissible compensation value, the transmission power is compensated on the basis of the generated power control information.
Thus, according to the transmission power control method for the mobile communication system, since the transmission is temporarily stopped if the generated control information is larger than the maximum permissible compensation value and resumes when the power control information becomes equal to or smaller than the maximum permissible compensation value, the transmission power can be prevented from being wasted.